Bonic acid ester stabilizing agent silver halide element containing a benzimidazoline 2 thione n n dicar

ABSTRACT

A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A FOGSTABILIZING AMOUNT OF A BENZIMIDAZOLINE-2-THIONE-N,N&#39;&#39;-DICARBONIC ACID ESTER.

United States Patent 3,761,278 SILVER HALIDE ELEMENT CONTAINING A BENZ- IMIDAZOLINE 2 THIONE-N,N'-DICARBONIC ACID ESTER STABILIZING AGENT Walter Gauss, Cologne, Anita von Konig and Franz Moll, Leverkuseu, Wolfgang Muller-Bardorlf, Cologne, and Wilhelm Saleck, Schildgenberg-Gladbach, Germany, assignors to Agfa-Gevaert Aktiengesellschaft, Leverkusen, Germany No Drawing. Filed Aug. 25, 1971, Ser. No. 174,930 Claims priority, application Germany, Aug. 27, 1970, P 20 42 533.8; June 18, 1971,P 21 30 031.2 Int. Cl. G03c 1/34 US. Cl. 96-109 3 Claims ABSTRACT OF THE DISCLOSURE A photographic silver halide emulsion containing a fogstabilizing amount of a benzimidazoline-2-thi'one-N,N-dicarbonic acid ester.

The invention relates to a photographic material comprising at least one silver halide emulsion layer the photographic properties of which have been improved by the addition of benzirnidazoline 2-thione-N,N'-dicarbonic acid esters.

As is well known, light-sensitive silver halide emulsions, especially those which have been chemically sensitized, tend to the formation of fog, i.e. nuclei which are capable of undergoing development without exposure, Fogging occurs especially at high temperatures and atmospheric humidity, if development is carried out for too long or at too high temperatures, if certain additives are used or if the emulsions are too strongly ripened, etc. The tendency of photographic silver halide emulsions to fogging can be suppressed to a certain extent by the addition of so-called stabilizers or antifogging agents. Compounds which have this elfect are e.g. heterocyclic mercapto compounds or inorganic or organic mercury compounds. The stabilizers have, however, the disadvantage that when used in effective concentrations they generally reduce the sensitivity of the stabilizing emulsions.

Another kind of fog is frequently formed in photographic materials comprising a paper support in particular a baryta-coated paper support. Upon processing of exposed photographic paper materials especially mechanical processes, thiosulfate frequently is carried from the fixing bath into the developing bath. In other cases, such as rapid-, stabilizingor fixing developing baths, a silver halide solvent, e.g. thiosulfate is added to the developing bath. When such thiosulfate-containing developing compositions are used in the development of photographic paper, a more or less pronounced yellow to brown fog is produced, depending on the type and age of the photographic paper. In the presence of some stabilizers, e.g., l-phenyl-S-mercapto-tetrazole, this fog may also be colored blue to blue violet. This fog consists of finely divided silver deposited in the barytes layer.

In barytes coated photographic papers, this yellow fog is due to silver salts which migrate during casting from the emulsion into the barytes layer where they are retained by adsorption. On storage of these finished papers, these silver salts are reduced to silver, a process which takes place particularly in the first months of storage. If silver halide solvents such as thiosulfates are added to the developer during the processing of the papers, the dissolved silver salts are reduced on the silver nuclei of the barytes-coating, and yellow fog and patches are produced.

After storage, the yellow fog is particularly pronounced on areas of the paper previously exposed to atmospheric moisture, e.g., at the edges of the paper and on the top sheet of a package.

3,761,278 Patented Sept. 25, 1973 The yellow fog occurs particularly when unrinsed emulsions of silver chloride or of silver chlorobromide are used because the chlorides present in excess can form soluble silver complex salts.

The yellow fog also occurs if types of gelatin containing compounds that dissolve silver halide are used in the production of the emulsion or of the baryta layer and if in addition there are present degradation products of gelatin which forms nuclei. These types of gelatin also produce a yellow fog in photographic films.

In addition, emulsions that have not been fully ripened and which have a steep gradation also tend to produce a yellow fogging, especially if high-contrast-developers with a high content of potassium bromide are used for developing the latent silver image.

It is among the object of the invention to provide stabilizers prevent the formation of any fog in photographic materials without concomitant undesired effects on the photographic properties. Another object of the invention is the production of photographic materials containing these agents.

We now have found a photographic material with at least one silver halide emulsion layer, which material contains benzimidazoline 2 thione-N,N'-dicarbonic acid esters.

Particular utility is exhibited by compounds of the following formula:

wherein represents:

The compounds shown in the following table have been found to be especially suitable.

TABLE Compound Number:

1 CzHs H 5,6-01 5-OCH3 5-Cl 5,6-01 5,6-01 5-G1 5-NO9 The compounds to be used according to the invention are prepared by reacting the benzimidazoline-Z-thione from which they are derived with pyrocarbonic acid esters, preferably in diluents.

PREPARATION OF COMPOUND 1 g. (1 mol) of Z-mercaptobenzimidazole, 500 ml. of ethanol and 405 g. (2.5 mol) of diethylpyrocarbonate are gradually heated to 50 C. and kept at this temperature until they dissolve. On the next day, 1.3 l. of petroleum ether are added, the reaction mixture is cooled for some time at -20 C. and the crystalline product obtained is removed by suction filtration and washed with petroleum ether which has been cooled to a low temperature. The crude product (187 g. M.P. 30 to 42 C.) is purified by dissolving it in a lukewarm mixture of 470 ml. of ethanol and 1.4 l. of petroleum ether, clarifying with charcoal and cooling to C. with stirring, and the diethylester of benzimidazoline-2-thione-N,Ndicarboxylic acid which precipitates is isolated. The product is now completely pure and melts at 65.5 to 66 C.

PREPARATION OF COMPOUND 2 21.9 g. (0.1 mol) of Z-mercapto-5,6-dichlorobenzimidazole, 40 ml. of ethanol, 48.6 g. (0.3 mol) of diethylpyrocarbonate and 0.5 ml. (0.001 mol) of 2 N sodium methylate solution are kept stirred overnight. The sandy reaction product obtained is removed by suction filtration (33.7 g., M.P. 109 to 113 C.) and recrystallised from ethanol. 25.5 g. of pure compound are obtained. M.P. 113-114 C.

PREPARATION OF COMPOUND 3 A suspension of 72.0 g. (0.4 mol) of 2-mercapto-5- methoxybenzimidazole and 388.8 g. (2.4 mol) of diethylpyrocarbonate is heated on a bath at a temperature of 90 C. A vigorous exothermic reaction sets in after about 2 hours, and at that moment the bath is removed. When the reaction has died down, the reaction mixture is again heated for 1 /2 hours on a bath which is at a temperature of 90 C. 400 ml. of ethanol are then added and the reaction mixture is then inoculated and left at 20 C. for complete crystallisation. The crystalline product is then removed by suction filtration and Washed with deep cooled ethanol. 94.4 g. of the diethylester of S-methoxybenzimidazoline 2 thione-N,N'-dicarboxylic acid, M.P. 76.5 to 77 C. are thus obtained. The product is purified by dissolving it in 4 times its quantity of hot ethanol, clarifying with charcoal and precipitating with 4 times the volume of hot light fraction petroleum hydrocarbons. The product then melts at 77.5 to 78 C.

PREPARATION OF COMPOUND 4 9.23 g. (0.05 mol) of Z-mercapto-S-chlorobenzimidazole, 20 ml. of n-propanol, 0.1 g. of the sodium salt of mono-n-propyl-carbonate and 28.5 g. (0.15 mol) of din-propylpyrocarbonate are stirred together, a solution being soon formed with evolution of CO On the next day, 70 ml. of petroleum ether are added and the reaction mixture is cooled to 20 C. and inoculated, and the product which then precipitates is removed by suction filtration after some time (3.4 g., M.P. 56 to 57 C.). After recrystallisation from petroleum ether (deep cooling) the product has a sharp melting point of 57 C.

PREPARATION OF COMPOUND 5 10.95 g. (0.05 mol) of 2-mercapto-5,6-dichlorobenzimidazole, 20 ml. of isopropanol, 0.1 g. of the sodium salt of monoisopropylcarbonate and 28.5 g. (0.15 mol) of diisopropyl pyrocarbonate are stirred together. A reaction sets in and CO is evolved. 0n the next day, the product is removed by suction filtration after it has been cooled to 20 C. and is then recrystallized from isopropanol. 12.0 g., M.P. 127.5 to 128 C., are obtained.

PREPARATION OF COMPOUND 6- 10.95 g. (0.05 mol) of 2-mercapto-5,6-dichloro-benzimidazole, 20 ml. of n-propanol, 0.1 g. of the sodium salt of mono-n-propylcarbonate and 28.5 g. (0.15 mol) of di-n-propylpyrocarbonate are stirred together, the original suspension being converted into the reaction product with evolution of CO On the next day, the crude product is removed by suction filtration at 0 C. (14.8 g., M.P. 80 to 805 C.) and recrystallized from acetonitrile. The compound then melts at 80.5 to 81 C.

PREPARATION OF COMPOUND 7 46.1 g. (0.25 mol) of 2 mercapto-S-chlorobenzimidazole. 135 ml. of ethanol, 97.2 g. (0.6 mol) of diethylpyrocarbonate and 1.25 ml. of 2 N sodium methylate solution are stirred together. A reaction sets in with evolution of CO On the next day, the product is removed by suction filtration and purified by recrystallisation from ethanol. 40.3 g. (M.P. 88.5 to 89 C.) are obtained.

PREPARATION OF COMPOUND 8 58.5 g. (0.3 mol) of Z-mercapto-S-nitrobenzimidazole and 243 g. (1.5 mol) of diethylpyrocarbonate are heated in an oil bath which is at a temperature of C. until they dissolve (2 hours). A paste is formed on cooling. It is removed by suction filtration at 0 C. and washed with alcohol. The resulting crude diethylester of 5-nitrobenzimidazoline 2 thione-N,N'-dicarboxylic acid, melting point C., is purified by recrystallizing it twice from 5 times its quantity of toluene. The product then melts at 138 to 138.5 C.

The photographic materials are prepared in accordance with common practice including the steps of:

1) Precipitation of the silver halide in the presence of a protective colloid and physical ripening;

(2) If desired removal as by washing from the resulting emulsion, the excess water-soluble salts that have formed as a result of the precipitation;

(3) Chemical ripening (after-ripening) the washed product to impart the desired sensitivity to the emulsion; and

(4) Applying the emulsion on a suitable support and drying.

The bisimidazoline compounds of the present invention can be added to any photographic layer within the photographic material. Preferably the stabilizers are added to a silver halide emulsion layer or to the baryta-coating depending somewhat on the desired effect. If fog inhibition in the silver halide emulsion layer is desired they are added preferably to an emulsion layer. On the other hand if the formation of yellow fog in the baryta-coating is to be prevented the stabilizers are preferably added to the baryta-coating. The stabilizers of the present invention, however, can also be incorporated into any other auxiliary photographic layer since in any case the compounds diffuse into the other layers of the photographic material during development. The auxiliary layers may be waterpermeable intermediate layer protective layers or as in the silver salt diffusion process it may also be an imagereceiving layer.

It depends on the desired effect and the photographic material to which layer the compound is to be added to obtain the optimum effect. This, however, can be found out easily by simple experiments customarily employed in the art.

The stabilizers can be added to the photographic layers at any stage of their production. They are added to the silver halide emulsions preferably after the chemical ripening to the casting solution for the emulsion layer. It is, however, also possible to add the stabilizers to the silver halide emulsion before chemical ripening.

The same holds true if they are to be added to the baryta-coating. Also in this case they can be added at any stage of the production of the baryta layer; for example: before, during or after heeding or mixing the baryta suspension.

The benzimidazoline compounds can be used in any silver halide emulsion. Suitable silver halides for the emulsion are silver chloride, silver bromide or mixtures thereof, if desired containing up to 10 mols-percent of silver iodide. The silver halides may be dispersed in the usual hydrophilic compounds such as carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, alginic acid and its salts, esters or amides or, preferably, gelatin.

The methods of incorporating the compounds in the photographic layers are relatively simple and well-known to those skilled in the photographic art. It is convenient to add the stabilizers from solutions in appropriate solvents whereby the solvent should be completely free from any deleterious elfect on the ultimate light-sensitive material. Suitable are in particular solvents miscible with water such as methanol, ethanol alone or in admixtures, tetra- 6 phenylolpropane or opaque supports such as paper, in particular baryta-coated paper which may be provided with hydrophobic layers of, for example, polyolefines such as polyethylene or polypropylene.

bleach process.

The photographic material may comprise any kind of 70 support customarily used for photographic materials. Suitable supports are, for example, transparent films of cellulose esters such as cellulose acetate, of polyesters in particular on the basis of polyethyleneglycol-terephthalic hydlofill'ane of acetone- The photographic materials can be processed by the The concentration of the stabilizers in the layers can usual processing techniques. Any photographic developer vary widely, for instance from about 1 mg. to 0.5 g-, or developer combination is operative for developing the preferably 22-200 mg. per mol silver. halide. In the exposed photographic material. The developer combaryta-coating the compounds are added in amounts of pounds can be added to a photographic layer or to the 0.01 to..-2.0 g., preferably 0.1 to 1.0 g. per kg. barium 1 aqueous processing bath. For example, it is possible to sulfate. The optimum concentration depends on the type use developers of the hydroquinone type, pyrocatechol of. the layer and on the effects desired. The optimum type, p-methylaminophenol, compounds of the l-phenylconcentration will be apparent to those skilled in the art pyrazolidone-3 series or phenylenediamine developers. upon making the tests and observations customarily The following examples illustrate the invention: employed in the art.

, The emulsions can also be optically sensitized with Example 1 cyaflmet rhodacyanme lgemcyamn? dyes such as A very highly sensitive silver iodobromide emulsion smbed by Hamel T cyamlfe Dy:s and and containing 5 mols percent of silver iodide is prepared in .l'elated p Intersclence Publlshers, the usual manner, the silver nitrate being introduced at The emulsions may also contain chemical sensitizFrst intervals into a solution which contains gelatin in addie.g. reducing agents such as stannous salts, polyamlnes tion to KI and K313 The emulsion i fl l t d i h such as diethyltriamine or sulfur compounds as described mohium lfat in a known manner and f e d f the in US. Pat. No. 1,574,944. For chemical sensitization, soluble salts one may further add to the given emulsions salts of noble h fluocg late i di d i warm water d h m t Such as ruthenium. rhodium, Palladium. iridium, required quantity of gelatin which contains sulfur is Platinum gold, as described in the article y added. The emulsion is then divided into several parts, lowsky, Wiss- Phot- 65-72 T emulsions the first part containing no additive whereas a stabilizer m y also contain p y y oxides, p ially p yis added to each of the other parts. Noble metal salts, ethylene oxide, and derivatives thereof, as chemical senpreferably gold salts, are then added to all the samples of sitizers. emulsion and the samples are ripened to their optimum The silver halide emulsions may additionally contain sensitivity. the usual stabilizers, e.g. homopolar or salt-type com- The emulsions are then prepared ready for casting by pounds of mercury with aromatic or heterocyclic rings, the addition of 200 mg. of 4-hydroxy-6-methyl-1,3,3a,7- such as mercaptotriazoles, simple mercury salts, sultetraazaindene as stabilizer, 600 mg. of saponin as wetting fonium mercury double salts, and other mercury comagent and 10 ml. of 10 percent aqueous solution of pounds. Other stabilizers which may be used include formaldehyde, the amounts being in each case based on azaindenes, especially tetraor penta-azaindenes, in par- 1 kg. of emulsion. The emulsion is cast on a layer support ticlllal' those Substituted with y amino p of cellulose acetate. Some of the film samples are stored Compounds of this type have been described in the article 40 at 60 f 3 d y Bin, WiSS- P other Suitable After exposure in a sensitometer customarily employed Stabilizers include 'y mercapto Compounds, in the art behind a step wedge, the emulsion layers are lphenyl's'mel'capto tetrazole, quaternary benlthiazole developed in a developer of the following composition: derivatives and benztriazoles.

The photographic layer may be hardened in the usual manner, for example, with formaldehyde or halogen-sub- Sod S fi nhy r s stituted aldehydes that contain a carboxyl group, e.g. Borax 7.0 mucobromic acid, diketones, methanesulfonic acid esters Hydroquinone 3.5 and dialdehydes. p-Monomethylaminophenol sulfate 3.5 The stabilizers which we have described may be used S di citrate 7,0 in various kinds of photographic emulsions. In addition potassium id 0,4 to being useful in X-ray and other non-optically sen- Made up with Water to 1 1 sitized emulsions they may also be used in ortho-chro- Developer temperature: 0 C. matic, panchromatic and infrared-sensitive emulsion. They may also be used for emulsions suitable for use in the The results of the SBIlSilIOlIlGiIiC test are shown in the silver salt diifusion process for color-photographic emulfollowing table.

-. TABLE 3 days heating, 7 development time 16' development time 7' development time Substance number l il r r l g f S, degree 7 Fog S, degree '7 Fog S, degree 7 Fog 1 0.25 0.28 1.25 0.4.1 1.10 0.54 5 +0.5 0.70 0.11 +0 090 0.14 +1.0 0. 90 0.10 a -1.0 1.00 0.28 -0.5 1.35 0.32 :l:0 1.25 0.38 5 +1.0 1.30 0.25 +0.5 1. 40 0.32 +1.0 1.50 0. 40 3 +1.0 1.10 0.24 +1.0 1.40 0.30 +1.0 1.50 0.40 a +1.0 1.30 0. 25 +1.0 1.60 0.32 i0 1.70 0.40

1No additive. NOTE.S=sensltivlty; -value; (3=1 shutter stop). sions and for photographic materials for the silver dye Example 2 An unrinsed silver chlorobromide gelatin emulsion (20 mol-percent silver bromide) containing per litre 0.18 mol silver halide, 20 ml. of a 10% aqueous solution of saponine and 2 m1. of a 30%} aqueous solution of formaldehyde is divided into several parts. To each sample is acid, of polycarbonates, preferably on the basis of bisadded a stabilizer of the present invention in form of a 1% solution in acetone. The added amounts are shown in the following table.

The samples of the emulsions are applied onto a barytacoated paper support and dried. The dried layers contain 1.5 to 1.6 g. silver in the form of silver halide pro m.

The samples, both fresh and after being stored for two days in a heating cupboard (60 C. and 40% relative humidity) are developed in the following developer:

Hydroquinone 6.0 1-phenyl-3-pyrazolidone 0.2 Sodium sulfite anhydrous 40.0 Sodium carbonate anhydrous 40.0 Potassium bromide 3.0 Sodium thiosulfate crystallized 3.0

Water up to 1 l.

The samples were developed at 2, 4 and 6 minutes at a temperature of 30 C.

The yellow fog of the different samples are measured with a densitometer customarily employed in the art behind a blue filter. The results are shown in the following table.

TABLE Yellow fog Fresh samples Heating cupboard developing time storage developing time Quantity Stabilizer in mgJl. 2 4 6 2 4 6 Control 0.16 0. 32 0.63 0. 32 0.57 0.71 30 0. 07 0. 12 O. 20 0. 07 0. 13 0. 20

Similar results are obtained in the materials are de veloped in the following developer:

pMethylaminophenolsulfate 1.3 Hydroquinone 3.0 Sodium sulfite anhydrous 13.0 Sodium carbonate anhydrous 15.0 Potassium bromide 1.0 Sodium thiosulfate crystallized 10.0

Water up to 1 1.

Development and measurement of the yellow fog is performed as described above. The results are shown in the following table.

It is readily apparent from the above tables, that the formation of yellow fog is substantially inhibited by the stabilizers. A control sample when fresh shows a slight yellow fogging and after being stored in the heating cupboard a strong brownish-yellow fogging was visible even after a development time of only 1 minute. If the emulsion layer is removed from the baryta-coating it can be observed that the baryta-coating of the control samples is brown in color while the baryta-coating of .the other test samples are colorless or only negligible colored..

EXAMPLE 3 A baryta-coating is applied from the following suspension:

Aqueous baryta paste (BaSO -content 'by The above suspension is divided into several parts. To these samples are added per kg. suspension 0.15 g. of stabilizers 1, 2, 5 and 6 in form of a 1% by weight aqueous solution of acetone. The raw paper is baryta-coated therewith three times in known manner. Thereafter an unrinsed silver chlorobromide emulsion as described in Example 2 is applied onto the baryta-coated paper support.

Processing and measurement of the yellow fog is accomplished as described in Example 1. Whereas the samples containing the stabilizers show no yellow fog after the heated cupbroad storage a dark brown, patchy yellow fog is visible with a control sample.

What is claimed is:

1. A light-sensitive photographic material having at least one support silver halide emulsion layer which contains a stabilizing amount of a benzimidazoline-2-thio ne- N,N-dicarbonic acid ester having the following formula:

wherein represents:

R straight chain or branched alkyl having up to 6 carbon atoms;

R hydrogen, alkyl having up to 6 carbon atoms, alkoxy having up to 6 carbon atoms, halogen, aroxy, nitro, carboxy, carbamoyl, sulfo or sulfamoyl and It 1 or 2.

2. Material of claim 1, wherein benzimidazoline-Z- thione-N,N'-dicarbonic acid ester is contained in the lightsensitive silver halide emulsion layer.

3. Photographic material of claim 1 including a barytacoated paper support wherein the benzimidazoline-2- thione-N,N'-dicarbonic acid ester is contained in the baryta-coating.

References Cited UNITED STATES PATENTS 3,026,201 3/1962 Rauch et al 96-109 X 3,364,028 1/1968 Von Konig 96-109 X NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, JR., Assistant Examiner US. Cl. X.R. 9676 

